Photographic diffusion transfer process for planographic printing



United States I PHGTOGRAPHIC DIFFUSION TRANSFER PRDC- ESS FOR PLANO-GRAPHIC PRINTING Wolfgang Liissig, Koln-Stammheim, and Eberhard Giinther, Leverkusen, Germany, assignors to Agra Aktiengesellschaft, Leveritusen, Germany, a corporation of Germany No Drawing. Filed Nov. 4, 1959, Ser. No. 350,769 Claims priority, application Germany Nov. '7, 1958 3 Claims. (Cl. 96-29) The present invention relates to planographic printing and more especially to planographic printing forms which are produced by transforming soluble silver complex salts which are imagewise distributed in a colloid layer, into hydrophobic greasy ink-receptive silver salt images.

In the production of a positive image of an original by the silver salt diffusion process, it is known that a silver halide emulsion layer (negative layer) of steep gradation after exposure under the original is developed by means of a silver halide developer solution while in contact with a so-called transfer layer (positive layer) which contains development nuclei such as for example colloidal silver sulphide, and a silver halide solvent, such as for example sodium thiosulphate.

A modification of the process consists in that the sodium thiosulphate is not added to the transfer layer, but to the silver halide developer solution.

In principle, the production of the images is based on the fact that unexposed and consequently undevelopable silver halide of the negative is dissolved by the silver halide solvent whereafter the soluble silver complex formed difiuses into the transfer layer. In this layer, the silver complex is reduced on the development nuclei by means of the silver halide developer solution to produce a metallic silver image which with respect to the original is positive and not laterally inverted.

In our copending United States patent application Serial No. 730,259, filed April 23, 1958, we have proposed processes which provide a subsequent chemical conversion of such silver images, produced by the silver salt diflusion process in or on the surface of a hydrophilic layer, into silver compounds capable of receiving greasy printing .ink, and thus permit the production of oitset planographic forms.

According to that application the image silver is first of all converted by oxidation into a sparingly soluble inorganic silver compound or into inorganic compounds of silver and/or of other heavy metals such as for example ferrocyanides, ferricyanides, silver chloride, silver bromide, silver oxide and others. Thereafter, by means of a second processing liquid, the silver ions and/or other heavy metal formed by the oxidation are reacted with organic compounds to form organic hydrophobic silver compounds which are more sparingly soluble than said in organic compounds, whereafter greasy printing ink is applied to said hydrophobic images. In this process, the silver serving for the production of the greasy ink-receptive image consequently experiences the following reactions:

It has now been found that these processes can be considerably simplified if, in the photographic production of the image, the reduction of the silver ions from the imagewise diffusing silver complexes is prevented by omitting the development nuclei in the positive layer, and instead directly reacting these silver ions after transfer into the positive layer by subsequent treatment with organic SH- compounds, to produce difficultly soluble organic hydrophobic silver compounds from said imagewise distributed silver salt complexes. An additional simplification is achieved in this way by omitting the thorough rinsing necessary according to the prior processes after production of the image (elimination of the residues of reducing developer which disturb the subsequent oxidation) and after the oxidation (elimination of the residues of oxidising agent which oxidise the SH-compounds).

In carrying through the present process a silver halide emulsion layer is exposed to the object to be reproduced, developed in a silver halide developer solution to produce a silver image and treated with a silver halide solvent to transform at least part of the unexposed silver halide into a soluble silver complex compound, which soluble silver complex compound is transferred to a colloid layer to produce a colloid layer containing therein in imagewise distribution said silver complex compound, whereafter said colloid layer is treated with an alkaline aqueous solution of an organic mercapto compound preferably containing an aliphatic hydrocarbon radical having 8 to 20 carbon atoms to transform said soluble silver complex compound into a positive image of the object to be reproduced consisting essentially of a hydrophobic silver compound of said mercapto compound, said hydrophobic silver compound image being then dyed with a greasy printing ink.

The negative materials and developers usually used in the production of silver images by the silver salt diffusion process are suitable for carrying out the present process. The silver halide emulsions of the negative layer are silver chloride emulsions, silver chlorobromide emulsions (1-99 percent AgCl+99-l percent of AgBr) and silver bromide emulsions, which may also contain small amounts of silver iodide (about 1-5 percent) although silver halide emulsion devoid of silver iodide are preferred. The best results are obtained with silver chloride emulsion and with silver chlorobromide emulsion, the silver halide of which contains not more than percent by weight of silver bromide. These emulsion layers may contain organic silver halide developers such as hydroquinone, p-methylaminophenol as it is well known in the art. The aqueous developer solutions usually contain an alkaline metal hydroxide, an organic silver halide developer substance such as hydroquinone, l-phenyl-3-pyrazolidone p-methylaminophenol, a preserving agent such as a watersoluble sulphite and silver halide solvents, such as for example sodium thiosulphate, potassium thiocyanate, ammonia or organic amine bases, the alkali metal thiosulphates being preferred. The pH value is about 9-13.

The positive layer serving as printing form is a hardened hydrophilic colloid layer applied to a paper or film support, the hydrophiiic colloid being preferably hardened gelatine (ll0 g./rn. If it is desired to keep the developer solution free from silver halide solvents or to decrease the amount of said solvents in the developer so lutions the colloid layer will have added thereto a sufiicient quantity of one of the aforesaid silver halide solvents preferably alkali metal thiosulphates (1-50 percent by weight as calculated on the amount of binding agent). In order to produce a good water conduction of the printing forms, addition of inert fillers, such as for example barium sulphate, strontium sulphate, may also be provided. This can in certain cases at least partially be replaced by the corresponding thiosulphates, which then simultaneously supply the thiosulphate ions for the transfer process. An improvement in the water conduction is also possible by aftertreatment with neutralised silicohydrofluo-ric acid according to the process of our copending United States patent application Serial No. 836,073, filed August 26, l959. The hardening of the positive layer may be effected by the ordinary hardening agents, preferably formaldehyde. These hardening agents are applied in such quantities that the positive layer after storage for 8 days at 40 C. melts within 3 to minutes .when immersed in boiling water.

The SH-compounds referred to in our copending United States patent application Serial No. 730,259 are suitable as organic compounds for transforming the soluble silver halide complexes into diiiiculty soluble hydrophobic organic silver compounds, but especially suitable are organic mercapto compounds which contain alkyl or .alkenylradicals, having 8 to carbon atoms and which are soluble in aqueous liquids containing up to 20 percent of n-pr-opanol and being adjusted to a pH value of about 11-14 by means of alkaline metal hydroxides such as sodium or potassium hydroxide, Such compounds correspond for instance to the general formula:

N ll R H s Z--- wherein Z represents one of the hetero atoms N and S which are present as ring elements of a heterocyclic compound selected from the group consisting of 5 and 6 membered hetcrocyclic compounds such as thiazoles, thiodiazoles, triazoles, imidazoles, pyrimidines.

7 R represents a normal or branched saturated or unsaturated aliphatic hydrocarbon radical with 8-20, preferably l220 carbon atoms, which is bonded directly or by means of additional linking members such as sulphur to one of the ring members of the heterocyclic compound. The following special compounds are to be mentioned Further suitable compounds correspond to the general formulae:

iuwhich formulae R stands for a saturated or unsaturated aliphatic hydrocarbon radical having 8 to 20 carbon atoms, R for lower alkyl having 1 to 4 carbon atoms and Me for an alkali metal such as sodium or potassium. Suitable compounds are by way of example:

The above mercapto compounds are usually applied in the form of 0.5-5 percent, preferably l3 percent, aqueous solutions being adjusted to a pH value of about 11-14 by means of alkali metal hydroxides such as sodium or potassium hydroxide. In the case of compounds which are not sufficiently soluble in such solutions, these may have added organic solvents which are miscible with water such as acetone, methanol, ethanol, n-propanol, these solvents being applied in amounts of up to 20 percent by volume as calculated on the water applied.

Example 1 A paper sheet having wet-strength properties and weighing about 140 gJm. is coated in a first working step with a gelatine solution having the following composition:

34 parts of aqueous 15 percent gelatiue solution 6 parts of an aqueous saturated solution of barium chloride 1 part of a 7.5 percent aqueous solution of saponine The solution is coated on the paper sheet and dried at C. to produce a layer of about 2-4 g./m v

In a second working step the gelatine layer is then treated with the following aqueous solution:

37 parts of water 3 parts of an aqueous lution 1.2 parts of an aqueous 10 percent sodium hydroxide solution 0.8 part of an aqueous 3 percent formalin solution 0.6 part of a 7.5 percent saponine solution Thereafter the gelatine layer is dried at 80 C. and the paper thus treated is stored for 8 days at 40 C.

To produce the printing form, a normal commercial negative paper as it is put on the market by AGFA AG. under the trade name Copyrapid is exposed by transmitted light or by reflected light to the object to be reproduced and this paper is then developed in contact with the above positive material in the following de- 50 percent sodium thiosulphate soveloper:

The papers are left in contact for about 20 seconds. Thereafter the positive is separated and it is treated for about 30 seconds with the solution of 10 g. of N -(N -octadecyl-semicarbazide)-dithiocarboxylic methyl ester in a mixture of 400 ml. 1 N sodium hydroxide 200 ml water, and

ml. n-propanol Thereafter the foil is thoroughly rinsed. The previously invisible image appears on linking the thus treated positive on the printing machine. At least 300 satisfactory prints are possible.

Example 2 The procedure is as in Example 1 with the variation that the positive after separation from the negative is treated with the solution of 10 g. of sodium dodecylxanthogenate, in 300 ml. of l N sodium hydroxide, and 300 ml. of water,

up to 200 prints are possible.

Example 3 The procedure is as in Example 1 with the variation that the positive after separation from the negative is treated with the solution of up to 200 prints are possible.

Example 4 The procedure is as in Example 1 with the variation that the positive after separation from the negative is treated with the solution of g. of 2-mercapto-5-dodecylmercapto-1,3,4-thiodiazole,

200 ml. of l N sodium hydroxide,

100 ml. of water, and

100 ml. of n-propanol,

up to 100 prints are possible.

Example 5 The procedure is as in Example 1 with the variation that the positive after separation from the negative is treated with the solution of 6 g. of 2-mercapto-4-heptadecyl-thiazole, in 100 ml. of 1 N sodium hydroxide,

100 m1. of water, and

100 ml. of n-propanol,

up to 200 prints are possible.

Example 6 The procedure is as in Example 1 with the variation that the positive after separation from the negative is treated with the solution of 6 g. of 1-amino-Z-mercapto-5-l1eptadecyl-1,3,4-triazole,

200 ml. of 1 N sodium hydroxide,

200 ml. of water, and

100 ml. of propanol,

up to 300 prints are possible.

Example 7 The procedure is as in Example 1 with the variation that the positive after separation from the negative is treated with the solution of 6 g. of l-octyl-2-mercapto-benzimidazole, in 300 ml. of l N sodium hydroxide,

100 ml. of water, and

50 ml. of n-propanol,

up to 200 prints are possible.

What is claimed is:

1. A process for the production of planographic printing forms which comprises exposing to an image a photographic silver halide emulsion in which at least 80% of the silver halide is silver chloride and the remaining silver halide is selected from the class consisting of silver chloride and silver bromide, contacting the exposed emulsion with a hardened gelatin layer containing alkaline earth thiosulphate, developing the exposed emulsion while in such contact with an alkaline aqueous silver halide developer to produce a negative of said image in the emulsion and to cause unexposed silver halide to dilluse into said gelatin layer as a silver complex, separating the emulsion from the gelatin layer, treating the resulting gelatin layer with an alkaline aqueous solution of a mercapto reactant selected from the class consisting of and S.Ra

wherein Z represents a hetero atom selected from the class consisting of nitrogen and sulfur, said hetero atom and the N and C to which it is connected forming a heterocyclic ring selected from the class consisting of thiazol, thiodiazol, triazol, imidazol, benzimidazol and pyrimidine; R and R stand for a member selected from the class consisting of an alkyl radical having 8-20 carbon atoms and mercapto alkyl, the alkyl group of which having 8-20 carbon atoms; R stands for lower alkyl and Me stands for an alkali metal, to transform the silver complex into a hydrophibic silver compound of said reactant and thereby make a positive hydrophobic image of the object, and inking the resulting product with a greasy printing ink.

2. A process for the production of planographic printing forms which comprises exposing a silver halide emulsion layer to an object being reproduced, the emulsion containing at least one silver halide compound selected from the class consisting of silver chloride, silver chloride containing up to 5 percent silver iodide, silver bromide, silver bromide containing not more than 5 percent silver iodide, and mixtures thereof, developing said exposed silver halide emulsion layer to produce therein a negative silver image of the object to be reproduced, and treating said layer with a silver halide solvent to transform at least part of the silver halide of the unexposed areas of said emulsion layer into a water-soluble silver salt complex while in contact with a transfer layer of hardened gelatin devoid of silver salt precipitating agents, and transferring said soluble silver salt complex to said transfer layer to produce therein an invisible positive silver salt complex image of the object to be reproduced, separating the negative layer and said transfer layer from each other and thereafter treating said transfer layer with an alkaline aqueous solution of an organic compound selected from the group consisting of compounds having the formulae l -R n-s-o-z---- heterocyclic ring selected from the class consisting of thiazol, thiodiazol, triazol, imidazol, benzimidazol and pyrimidine; R and R stand for a member selected from the class consisting of an alkyl radical having 8-20 carbon atoms and mereapto alkyl, the alkyl group of which having 8-20 carbon atoms; R stands for lower alkyl and Me stands for an alkali metal, to transform said imagewise distributed soluble silver complex into a hydrophobic silver compound of said organic compound so as to make said positive image receptive for greasy printing inks, and inking the resulting layer with said printing ink.

3. A process according to claim 2, wherein said colloid layer contains at least one compound selected from the group consisting of alkaline earth metal sulphates and thiosulphates.

References Cited in the file of this patent UNITED STATES PATENTS 1,742,710 Krebs Jan. 7, 1930 2,740,717 Yutzy et a1. Apr. 3, 1956 FQREIGN PATENTS 648,897 Great Britain Jan. 17, 1951 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nor 3 O63 837 November 13 1962 Wolfgang Lassig et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected belown Column 3, line 10 for "difficulty" read difficultly column 3 lines 55 to 60 the double bond between the carbon atom and the SH-group in the formula should be replaced with a single bond; column 5 line 3 for ""hydr-ozine read hydrazinecolumn 6 line 29, for "hydrophibic" read hydrophobic "*a Signed and sealed this 6th day of August 19630 (SEAL) fattest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A PROCES FOR THE PRODUCTION OF PLANOGRAPHIC PRINTING FORMS WHICH COMPRISES EXPOSING TO AN IMAGE A PHOTO-GRAPHIC SILVER HALIDE EMULSION IN WHICH AT LEAST 80% OFF THE SILVER HALIDE IS SILVER CHLORIDE AND THE REMAINING SILVERR HALIDE IS SELECTED FROM THE CLASS CONSISTING OF SILVER CHLORIDE AND SILVER BROMIDE, CONTACTING THE EXPOSED EMUL-SION WITH A HARDENED GELATIN LAYER CONTAINING ALKALINENE EARTH THIOSULPHATE, DEVELOPING THE EXPOSED EMULSION WHILEE IN SUCH CONTACT WITH AN ALKALINE AQUEOUS SILVER HALIDEE DEVELOPER TO PRODUCE A NEGATIVE OF SAID IMAGE IN THEE EMULSION AND TO CAUSE UNEXPOSED SILVER HALIDE TO DIFFUSEE INTO SAID GELATIN LAYER AS A SILVER COMPLEX, SEPARATING THEE EMULSION FROM THE GELATIN LAYER, TREATING THE RESULTINGNG GELATIN LAYER WITH AN ALKALINE AQUEOUS SOLUTION OF AOF A MERCAPTO REACTANT SELECTED FROM THE CLASS CONSISTING OFF 